The two main reasons or causes of some species of organisms being threatened by extinction is because of the loss of genetic variation and loss pf habitat which occurs both naturally and because of human activities. Hunting is also a reason for species of that particular organism to be endangered. This will have a great effect to the environment, why? Because, aren't the species themselves are part of the environment? That just means that every single specie that goes extinct, a part of the environment dies. The disappearance of a particular specie of organisms could lead to a cascade of other species going to extinct as well.